The present invention relates to vehicle occupant restraint systems, and more particularly, to an improved fluid supply for use with such restraint systems.
In general, vehicle occupant restraint systems utilize some type of a crash sensor which senses the rapid deceleration which occurs when the vehicle is involved in a collision. The collision signal from the sensor actuates a fluid supply or inflator system which provides a quantity of inflation gas to inflate an expandable confinement which restrains the vehicle occupant. The restraint systems of the class described may be positioned in the dashboard for deployment in the passenger compartment of the vehicle, or may have the inflator and confinement portion of the system located on the steering wheel to deploy and restrain the driver. In the latter case, it is necessary that the fluid supply fit compactly adjacent the steering wheel hub, without extending too far toward the driver, or radially toward the rim of the steering wheel. Therefore, while the present invention is equally adapted for any occupant restraint system, it is especially useful for such a system which is located on the steering wheel, and will be described in connection therewith. It is also especially adapted for systems which utilize the combustion of gas generating material as the source of the inflation gas.
Among the prior art fluid supplies for occupant restraint systems are those exemplified by German Pat. No. 2,325,310, in which the generated gas flows radially out of a cylindrical housing. Another type of fluid supply is exemplified by U.S. application Ser. No. 459,529, which issued Oct. 5, 1976, as U.S. Pat. No. 3,984,126 filed Apr. 4, 1974 and assigned to the assignee of the present invention, showing a generally cylindrical housing from which the generated gas flows axially out of one end of a cylindrical housing and is then deflected radially. Among the common features of most such prior art fluid supplies are the inclusion of a mass of combustible gas generating material and some type of filter disposed between the combustible material and the fluid discharge port defined by the housing.
Among the problems associated with the prior art fluid supplies has been the tendency for the filters to become clogged with the fine particles of fly ash which comprise a certain, relatively small percent of the combustion product when the gas generating material burns. If sufficient clogging of the filter occurs, the flow area through which the generating gas is discharged may be restricted to the point that excessive pressure builds up within the housing, thus presenting the possibility of the fluid supply housing bursting rather than directing a controlled volume of filtered inflating gas into the confinement. As a result, it has been necessary to increase the strength of the housing to withstand the higher pressures, typically by increasing the thickness of the steel normally used for the housing.
In the course of development of fluid supplies, it has been found that among the combustion products formed by the burning of the gas generating material are solid "clinkers" or "sinters" which are burned particles of approximately the same size as the original granules of combustible material. It has further been found that the clinkers are desirable in that they are easier to retain and they filter some of the fine fly ash, thus preventing it from reaching the final-stage filter, i.e., the filter adjacent the fluid discharge ports.